The present invention relates to a method of forming Si3N4 and SiO2 thin film by utilizing atomic layer deposition method and employing trisdimethylaminosilane {HSi[N(CH3)2]3}, (hereinafter, referred to as xe2x80x9cTDMASxe2x80x9d) as a reactant.
Generally, Si3N4 and SiO2 thin films are formed in semiconductor devices by utilizing deposition methods such as Chemical Vapor Deposition (CVD), Low Pressure Chemical Vapor Deposition (LPCVD), plasma-enhanced chemical vapor deposition (PECVD).
CVD-based methods often have drawbacks that limit their usefulness in the manufacture of semiconductor devices that would benefit by inclusion of thin films of Si3N4. In a typical CVD method, a thin film of Si3N4 is deposited at a relatively high temperature, which in general is less preferable than a lower temperature process due to the possibility of adverse thermal effects on the device. A Si3N4 layer deposited by CVD is also subject to geometric hindrances causing thickness variations across the surface of the device. The thickness of the thin film formed around densely packed features on the surface can be less than the thickness of the film around less densely packed features. This problem is known as a pattern loading effect.
LPCVD suffers from shortcomings as well. The hydrogen content of the LPCVD-manufactured thin film is usually high, and step coverage of the surface is not good. Since the film growth rate is relatively slow when using LPCVD, the processing time required to grow a film of suitable thickness is relatively long. The long processing time exposes the substrate to a relatively high temperature for a long time, and results in a high thermal budget associated with the LPCVD process.
Atomic layer deposition (ALD) has been proposed as an alternative to CVD-based depositions methods for the formation of Si3N4 and SiO2 thin films. ALD is a surface controlled process conducted in a surface kinetic regime, and which results in two-dimensional layer-by-layer deposition on the surface. Goto et al. describe an ALD deposition method using dichlorosilane (DCS) and NH3 plasma to form a Si3N4 film. (Appl. Surf. Sci., 112, 75-81 (1997); Appl. Phys. Lett. 68(23), 3257-9(1996)). However, the properties of the thin film manufactured by the method described in Goto are not suitable. The Cl content (0.5%), and O content are unacceptably high. These, combined with a measured Si:N ratio of 41:37 indicate that this method does not form a near-stoichiometric film of Si3N4. In addition, the growth rate of 0.91 angstroms per cycle of 300 seconds is not as high as would be necessary for commercial applications.
Klaus et al. describe an ALD method of forming a Si3N4 film by reacting SiCl4 and NH3. See, U.S. Pat. No. 6,090,442, and Surf. Sci., 418, L14-L19 (1998). The characteristics of the thin film manufactured by this method are better than that achieved by Goto et al. The ratio of Si:N=1:1.39, and the Cl, H and O contents are acceptably low. However, the cycle time of 10 minutes to grow a 2.45-angstrom film is too long, making any commercial application impractical.
It has also been proposed to use Si2Cl6 (HCD) and N2H4 to deposit a thin Si3N4 film by ALD. (Appl. Surf. Sci., 112, 198-203 (1997)). While the stoichiometry, Cl and H content of such films are suitable, they exhibit an unacceptably high oxygen content, rendering such films unsuitable for the uses described above.
ALD has also been proposed as a method of depositing SiO2 thin films. For example, it has been proposed to depositing process using SiCl4 and H2O. Appl. Phys. Lett. 70(9), 1092 (1997). However, the cycle time in the proposed process is too long for commercial application. U.S. Pat. No. 6,090,442 discloses a catalyzed process wherein a SiO2 film is deposited using SiCl4 and H2O, with C5H5N or NH3 as a catalyst. The quality of the SiO2 film obtained with this process is not good because of the low deposition temperatures. A process utilizing Si(NCO)4 and TEA has been proposed (Appl. Surf. Sci. Vol. 130-132, pp. 202-207 (1998)), but also suffers from low quality due to low processing temperatures. The same is true of a proposed process using Si(NCO)x, and H2O, (J. Non-crystalline Solids, Vol. 187, 66-69(1995)).
Therefore, despite a long-recognized potential for widespread application, a need remains for a novel method of forming Si3N4 and SiO2 thin films that meet the following criteria: low thermal budget process; excellent step coverage; no pattern loading effect; Si:N ratio consistent with Si3N4; excellent thickness control and uniformity; minimal number of particulate inclusions; low impurity content; and a film growth rate that makes commercial application practical.
In order to accomplish the above-described items, an atomic layer deposition (ALD) employing TDMAS as a reactant is utilized for the preparation of Si3N4 and SiO2 thin films in the present invention.
The present invention is embodied in an atomic layer deposition method of forming a solid thin film layer containing silicon in which a substrate is loaded into a chamber. A first reactant containing Si and an aminosilane is injected into the chamber, where a first portion of the first reactant is chemisorbed onto the substrate, and a second portion of the first reactant is physisorbed onto the substrate. The physisorbed second portion of the first reactant is then removed from the substrate, by purging and flushing the chamber in one preferred embodiment. A second reactant is then injected into the chamber, where a first portion of the second reactant is chemically reacted with the chemisorbed first portion of the first reactant to form a silicon-containing solid on the substrate. The non-chemically reacted portion of the second reactant is then removed from the chamber. In one preferred embodiment, the silicon-containing solid formed on the substrate is a thin film layer, a silicon nitride layer for example. In other preferred embodiments, the first reactant is at least one selected from the group consisting of Si[N(CH3)2]4, SiH[N(CH3)2]3, SiH2[N(CH3)2]2 and SiH3[N(CH3)2]. The second reactant is preferably activated NH3. The chamber pressure is preferably maintained in a range of 0.01-100 torr. and in preferred embodiments can be maintained constant throughout the process, or can be varied in at least one of the four steps. One or more of the foregoing steps can be repeated to achieve a thicker solid on the substrate.
In various embodiments, silicon-containing solids formed by the methods of the invention have a dry etch selectivity with respect to Si of a semiconductor device when formed as an active mask nitride, with respect to WSix and doped poly-Si of a semiconductor device when formed as a gate mask nitride, and with respect to W and Ti/TiN of a semiconductor device when formed as a bit line mask nitride. The silicon-containing solid formed on the substrate can also be formed to act as a CMP stopper, or as an insulating layer having a dry etch selectivity with respect to SiO2 of a semiconductor device (spacer). In other embodiments, the silicon-containing solid formed on the substrate is an insulating layer having an HF wet etch selectivity with respect to SiO2 of a semiconductor device to act as a wet stopper.
The silicon-containing solid formed on the substrate can serve as a gate dielectric of a semiconductor device, a layer formed between a Ta2O5 layer and a capacitor storage node of a semiconductor device, as a dielectric layer of a capacitor of a semiconductor device, or as an STI liner of a semiconductor device.
In other embodiments, the silicon-containing solid formed on the substrate is silicon oxide, and in one or more of those embodiments the second reactant is selected from the group consisting of H2O, H2O2, O2 plasma and O3 plasma.
In yet another embodiment, at least one of the first and second silicon-containing solids is a metal silicate wherein the metal is selected from the group consisting of Al, Hf, Zr, Ti, and Ta.
These and other features of the invention will now be described with reference to the drawings.